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首页> 外文期刊>Journal of Applied Crystallography >Anomalous neutron scattering 'halo' observed in hignly oriented pyrolytic graphite
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Anomalous neutron scattering 'halo' observed in hignly oriented pyrolytic graphite

机译：在静脉定向的热解石墨中观察到异常的中子散射'晕圈'

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摘要

Highly oriented pyrolytic graphite (HOPG) has been used as monochromators, analyzers and filters at neutron and X-ray scattering facilities for more than half a century. Interesting questions remain. In this work, the first observation of anomalous neutron 'halo' scattering of HOPG is reported. The scattering projects a ring onto the detector with a half-cone angle of 12.4 degrees, which surprisingly persists to incident neutron wavelengths far beyond the Bragg cutoff for graphite (6.71 angstrom). At longer wavelengths the ring is clearly a doublet with a splitting roughly proportional to wavelength. Sample tilting leads to the shift of the ring, which is wavelength dependent with longer wavelengths providing a smaller difference between the ring shift and the sample tilting. The ring broadens and weakens with decreasing HOPG quality. The lattice dynamics of graphite play a role in causing the scattering ring, as shown by the fact that the ring vanishes once the sample is cooled to 30 K. A possible interpretation by multiple scattering including elastic and inelastic processes is proposed.
机译：高度导向的热解石墨（HOPG）已被用作中子和X射线散射设施的单色器，分析仪和过滤器，超过半个半个世纪。有趣的问题仍然存在。在这项工作中，据报道了霍普格的异常中子晕晕散射的第一次观察。散射将环突出到检测器上，半锥角为12.4度，这令人惊讶地持续到远远超过石墨（6.71埃）的布拉格截止的入射中子波长。在较长的波长下，环显然是双重的，具有与波长大致成比例的分裂。样品倾斜导致环的偏移，其是波长与较长波长相关的波长，在环形换档和样品倾斜之间提供较小的差异。环宽度扩大和削弱，随着HOPG质量的降低。石墨的晶格动力学在引起散射环的情况下发挥作用，如将样品冷却到30K后，环消失的事实所示。提出了多个散射的可能解释，包括弹性和无弹性过程。

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